Mayweather Jr last fought in December 2007
Floyd Mayweather Jr has postponed his comeback fight against lightweight champion Juan Manuel Marquez after suffering a rib injury in training.
The undefeated five-division champion, who has not fought since beating Ricky Hatton in 2007, was due to fight three-weight champion Marquez on 18 July.
"I am extremely disappointed that this fight has to be postponed," Mayweather said in a statement.
"I was training very hard and looking forward to getting back in the ring."
Mexican Marquez, from his training camp, added: "I was very disappointed to hear the news about the fight being postponed.
"I will remain focused, in shape and ready to fight whenever the fight is rescheduled for."
Mayweather and Marquez had been due to fight at the MGM Grand Garden Arena in the American's hometown of Las Vegas.